JPS5843953B2 - Color video signal recording and playback method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an FM signal obtained by FM modulating a composite color video signal.
The present invention relates to a method for recording and reproducing a color video signal by recording and reproducing a modulated signal on a VTR or the like.

Conventionally, there are various methods for magnetically recording composite color video signals on a VTR, and one of the FM magnetic recording methods is a high-band magnetic recording method.

This is a composite color video signal of 7.06MHz as it is.
The system performs FM modulation in a frequency range of 10 MHz to 10 MHz, and records this FM modulated composite color video signal on a magnetic tape using a VTR.

By the way, when a magnetically recorded signal is regenerated in this way, the reproduced signal is FM demodulated, and a burst signal is extracted from the composite color video signal that is the FM demodulated output, the S/N of the burst signal may be poor. , it has been extremely difficult to reproduce images with good color because they include time axis errors.

Therefore, conventionally, only the color burst signal in the composite color video signal has its frequency (3.58 M in the case of NTSC system).
Hz) to a frequency of 100,000 Hz, the entire composite color video signal is FM modulated, recorded on a magnetic tape with a VTR, and then played back and FM demodulated to obtain a composite color video signal. Double the frequency of the color burst signal in the video signal to the original frequency (3.58MHz)
I was trying to change it back to .

In this way, the time axis error of the reproduced color burst signal obtained at the end was only 100 compared to that without the above-mentioned processing, and was not much improved.

However, such a method not only complicates the circuitry of the recording/reproducing system of the VTR, but also makes it impossible to reliably correct the time axis error of the color burst signal.

In view of the above, the present invention proposes a method for recording and reproducing color video signals that can reliably improve the S/N ratio of color burst signals in composite color video signals and correct time axis errors. It is.

In the present invention, when recording an FM modulated signal obtained by FM modulating a composite color video signal, the carrier frequency of the FM modulated signal is set to an integral multiple of the frequency of the color burst signal in the composite color video signal. It is to be selected.

Furthermore, the reproduced FM modulated signal obtained by reproducing the recorded recording signal is FM demodulated to obtain an FM demodulated composite color video signal, and the color burst signal in this FM demodulated composite color video signal is reproduced as a reproduced FM modulated signal. The time axis is corrected in the signal portion of the carrier frequency in the modulated signal.

Hereinafter, an embodiment in which the present invention is applied to a high-band recording type VTR will be described in detail with reference to FIGS. 1 to 4.

Figure 1 shows a VTR to which the F~■ magnetic recording method of the present invention is applied.
This shows the recording system.

tl is an input terminal to which a composite color video signal is supplied, and this input terminal t is the input terminal of the clamp circuit 1, the synchronization separation circuit 5 for separating the horizontal synchronization signal, and the APC circuit (automatic phase control circuit) 6. connected to the end.

The output end of the clamp circuit 1 is connected to the input end of the FM modulator 2, and the output end thereof is connected to the output terminal t2.
It is connected to the input terminal of the gate circuit 3.

The clamp circuit 1 is composed of a capacitor C1 and an on/off switch SW1.

The output terminal of the synchronous circuit 5 is connected to one input terminal of the gate circuit 3, the sample hold circuit 10, and the APC circuit 6.

The sample hold circuit 10 is composed of a capacitor C2 and an on/off switch SW2.

The output terminal of the APC circuit 6 is connected to a phase detector 8 via a multiplier 7.
The output terminal of the gate circuit 3 is also connected to the other input of the phase shifter 8.

The output end of the phase detector 8 is connected to the input end of a sample-and-hold circuit 10 via a low-pass wave detector 9.

The output end of the sample hold circuit 10 is connected to the other input end of the clamp circuit 1 via the DC amplifier 4.

The APC circuit 6 consists of a gate signal generation circuit 11, a burst gate circuit 12, and an APC loop circuit 16, and the APC loop circuit 16 has an oscillation frequency of 3.58 MH.
It consists of a voltage controlled oscillation circuit 13, a phase comparator 14, and a low-pass wave transducer 15.

Next, the operation of the recording system shown in FIG. 1 will be explained with reference to FIG. 2 as well.

In this FIG. 2, C to G are shown with time enlarged relative to A and B.

First, the input terminal t1 is supplied with a composite color video signal as shown in FIG.

The composite color video signal is connected to capacitor C3 of clamp circuit 1.
The sync tip portion 17 of the horizontal synchronizing signal is clamped to a predetermined level by the output of the DC amplifier 4.

The horizontal synchronization signal extracted by the synchronization separation circuit 5 is supplied to the gate signal generation circuit 11 of the APC circuit 6, where the burst signal sampling pulse shown in FIG. 2C is generated.

By supplying this burst signal extracting pulse to the burst gate circuit 12, only the color burst signal portion 19 in the composite color video signal shown in FIG. 2A supplied to the input terminal t1 becomes as shown in the second diagram. is extracted as its output.

The oscillation output signal of the voltage-controlled oscillator circuit 13 is supplied together with the output signal of the burst gate circuit 12 to a phase comparator 14 , where these signals are compared in phase, and the output thereof is supplied to a low-pass wave current filter 15 . be done.

If there is a phase difference between these signals, the output voltage from the low-pass waveform generator 15 is supplied to the voltage-controlled oscillation circuit 13 and its frequency is controlled depending on the magnitude of the phase difference.

FIG. 2 E obtained as the output of the voltage controlled oscillation circuit 13
The continuous wave signal with a frequency of 358 MHz shown in FIG.
The signal will be as shown in .

On the other hand, the FM modulated signal of the composite color video signal shown in FIG. 2B is obtained as the output of the FM modulator 2.

This FM modulated signal is supplied to the gate circuit 3, where it is gated by the horizontal synchronization signal shown in FIG.
As an output, a signal shown in the second diagram corresponding to the sync chip portion 18 in FIG. 2B, that is, a carrier wave signal of the FM modulated signal is obtained.

In the case of this example, the frequency of this signal is 7.16 M
It is Hz.

The output signal from the gate circuit 3 and the output signal from the multiplier 7 are supplied to a phase comparator 8.

When there is a phase difference of θ, for example 90' (7), between these signals, the DC output voltage of the low-pass filter 9 is a certain value, and the phase difference between these signals is θ. When it is ±α, a predetermined DC output voltage is obtained from the low-pass wave current generator 9 according to the magnitude of ±α.

This DC output voltage of the low-pass waveformer 9 is supplied to a sample-and-hold circuit 10.

In the sample and hold circuit 10, the horizontal synchronization signal from the synchronization separation circuit 5 is supplied to the on-off switch SW2 as a switching signal, so that the on-off switch SW2 is closed only during the period of the synchronization signal, and the output of the low-pass filter 9 Capacitor C2 is charged.

The DC voltage as the output of the sample and hold circuit 10 is supplied to the DC amplifier 4, where it is compared with the voltage of a reference power supply provided within the DC amplifier 4.

The synchronization signal from the synchronization separation circuit 5 is the on-off switch SW
1 as a switching signal, the on/off switch SW1 is closed only during the period of the horizontal synchronization signal.

As a result, the output voltage of the DC amplifier 4 is superimposed on the sync tip portion 17 in FIG. 2A, resulting in a voltage as shown at 18 in FIG. 2B.

At this time, the FM modulated signal of the composite color video signal shown in FIG. 2B is obtained as the output of the FM modulator 2.

In this FM modulated signal, the portion corresponding to the sync chip portion 18 in FIG. 2B becomes a signal with the waveform shown in FIG. The phase is delayed by θ, in this case 90°, compared to the output signal of the multiplier 7 shown in FIG. 2F.

That is, the output voltage of the sample and hold circuit 10 is compared with the voltage of the reference power supply by the DC amplifier 4, and the output of the DC amplifier 4 is supplied to the FM modulator 2 via the clamp circuit 1. The phase difference between the output signal of the circuit 3 and the output signal of the multiplier 7 is θ, for example, ±90'E with a center of 9 o%.
Made to be within range.

Then, the phase of the carrier wave of the FM modulated signal is constrained by the operations of the phase comparator 8, sample hold circuit 10, DC amplifier 4, clamp circuit 1, FM modulator 2, etc.
Its phase is delayed by θ, for example, by 90, compared to the output signal of the multiplier 7, that is, the phase of the signal obtained by doubling the color burst signal 19 of the composite color video signal shown in FIG. 2A, which is supplied to the input terminal t1. Ru.

Furthermore, the carrier wave frequency of this FM modulated signal obtained at the output terminal t2 is selected to be an integral multiple of the frequency of the color burst signal in the color video signal, 3.58 MHz, twice in this example, and is 7.16 MHz. It is.

Note that this FM modulated signal is obtained by pre-emphasizing the high frequency components of the modulated signal by the FM modulator 2.

Next, a reproduction system of a VTR to which the present invention is applied will be explained with reference to FIGS. 3 and 4.

FIG. 3 shows a reproduction system of a VTR to which the present invention is applied.

In FIG. 3, t3 is an input terminal of the reproduction system, and a reproduced FM modulated signal obtained by reproducing a recording signal recorded by the above-mentioned FM magnetic recording method is supplied here.

The input terminal t3 is connected to the input terminals of the FM demodulator 20 and the gate circuit 22, and the output terminal of the FM demodulator 20 is connected to the sync separation circuit 21. Output terminal t4 connected to the input end of the gate circuit 23 and supplied with the reproduced composite color video signal
connected to.

The output terminal of the synchronous separation circuit 21 is connected to the gate signal input terminal of the gate circuit 22, and the gate signal generation circuit 35
connected to the input end of the

The output terminal of the gate signal generation circuit 35 is connected to the gate signal input terminal of the gate circuit 23.

The output end of the gate circuit 22 has a center frequency of 7.16 MH
It is connected to the input end of a waveform shaping circuit 25 via a narrow band pass transducer 24 of z.

The output end of the gate circuit 23 is connected to the input end of the limiter circuit 26.

The output terminals of the limiter circuit 26 and the waveform shaping circuit 25 are respectively connected to the D terminal and the T terminal of the D-type flip-flop circuit 27, and the output terminal thereof is an output terminal from which a color burst signal is obtained via a phase shifter 36. t, is connected to.

Next, the operation of the reproduction system shown in FIG. 3 will be explained with reference to the waveform diagram in FIG. 4.

The reproduced FM modulated signal shown in FIG. 4A supplied to the input terminal t3 is supplied to the FM demodulator 20 and demodulated, resulting in a signal having the waveform shown in FIG. 4B.

In this waveform, the rising and falling portions 28.2 of the synchronization signal 30
9 is different from the rising and falling portions of the synchronization signal in the modulation signal shown in FIG. 2B, but this is because they are pre-emphasized during modulation.

The signal shown in FIG. 4B is supplied to the synchronization separation circuit 21, and
A gate signal shown in FIG. 4C is obtained at one output end of the synchronization separation circuit 21, and this gate signal is supplied to the gate circuit 22.

On the other hand, from the input terminal t3, the FM modulated signal shown in FIG. As an output, a signal having the waveform shown in the fourth diagram is obtained.

This signal is obtained by removing a portion 31 whose frequency is lower than the carrier frequency due to the influence of pre-emphasis in the signal of the portion corresponding to the synchronization signal of the FM modulated signal shown in FIG. 4A, and the frequency is equal to carrier frequency 7.1
6 MHz.

The signal shown in this fourth diagram has a center frequency of 7.16 MH
z to a narrowband filter 24, the output of which is the sinusoidal signal shown in FIG. 4E having a frequency of exactly 7.16 MHz.

The signal shown in FIG. 4E is supplied to the waveform shaping circuit 25, where the amplitude is limited to become the signal shown in FIG. 4G, which is supplied to the T terminal of the D-type flip-flop circuit 27.

On the other hand, the synchronization signal obtained at the other output terminal of the synchronization separation circuit 21 is supplied to the gate signal generation circuit 35, and the gate signal generation circuit 35 generates a color burst signal extraction pulse.

This color burst signal sampling pulse is sent to the gate circuit 23.
supplied to

The demodulated output signal shown in FIG. 4B from the FM demodulator 20 is supplied to the gate circuit 23, where the gate signal generation circuit 3
It is gated by the color burst signal extraction pulse supplied from 5.

Since the color burst signal 32 of the demodulated composite color video signal shown in FIG. 4B is affected by jitter,
Many noise components are included, and the waveform of the output signal of the gate circuit 23 is as shown in FIG. 4F.

This signal is supplied to the limiter circuit 26 to limit its amplitude, and then supplied to the D terminal of the D-type flip-flop circuit 27.

The D-type flip-flop circuit 27 is triggered at the rising edge 33 of the signal having the waveform shown in FIG. 4G, which is supplied from the waveform shaping circuit 25 to the T terminal.

When the trigger signal is supplied to the T terminal, the D-type flip-flop circuit 27 maintains the level of the signal supplied to the D terminal and outputs a signal having the waveform shown in FIG. 4H at a frequency of 3658 MHz to its output terminal. occurs.

The signal with the waveform shown in FIG. 4G, which is supplied to the T terminal of the D-type flip-flop circuit 27, is generated from the carrier wave signal of the FM modulated signal shown in FIG. The phase is delayed by θ, for example, 90°, compared to a signal obtained by doubling the burst signal.

Therefore, the phase of the signal having the waveform shown in FIG. 4G is delayed by .theta., for example, 90.degree., and the phase of the signal having the waveform shown in FIG. 4H is delayed by 7, for example, 45.degree..theta..

The signal shown in FIG. 4H is supplied to the phase shifter 28 which advances the phase by seven, and the phase is reversed, so that the color burst signal with few noise components shown in FIG. 4 is obtained at the output terminal t5.

On the other hand, the composite color video signal demodulated by the FM demodulator 20 is obtained at the other output terminal t4.

Therefore, in this reproduction system, the reproduced FM modulated signal shown in FIG. 4A obtained by reproducing the recorded signal is FM demodulated, and the color in the FM demodulated composite color video signal shown in FIG. The time axis of the burst signal 32 is corrected using the signal portion of the carrier frequency in the reproduced FM modulated signal shown in FIG. 4A.

According to the above-described method for recording and reproducing color video signals of the present invention, the carrier frequency of the FM modulated signal is selected to be an integral multiple of the frequency of the color burst signal in the composite color video signal, and the FM of the recorded signal is adjusted during reproduction. Since the color burst signal in the composite color video signal that is the demodulated output is time-axis corrected at the signal portion of the carrier frequency in the reproduced FM modulated signal, the S/N ratio is improved and the time-axis error is reliably corrected. It is possible to obtain a burst signal.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of an embodiment of a recording system of VTil to which the present invention is applied, Fig. 2 is a waveform diagram for explaining the operation of Fig. 1, and Fig. 3 is a reproduction system of a VTR to which the present invention is applied. FIG. 4 is a system diagram of one embodiment of the present invention, and is a waveform diagram for explaining the operation of FIG. 3.

Claims (1)

[Claims] 1. When recording the FM modulated signal obtained by FM modulating the composite color video signal, the carrier frequency of the FM modulated signal is selected to be an integral multiple of the frequency of the color burst signal in the composite color video signal, and the reproduction is performed. FM demodulating the time-reproduced FM modulated signal to obtain an FM demodulated composite color video signal;
A method for recording and reproducing a color video signal, characterized in that a color burst signal in the FM demodulated composite color video signal is time-base corrected using a signal portion of a carrier frequency in the reproduced FM modulated signal.